1. Field of the Invention
The present invention relates to improved knife blade apparatus for severing rupture disks, and more particularly, but not by way of limitation, to an improved knife blade apparatus adapted to be installed in a reverse buckling rupture disk assembly.
2. Description of the Prior Art
Rupture disk assemblies which include reverse buckling rupture disks and knife blades have been developed and used heretofore. In operation of such an assembly, when the reverse buckling rupture disk reverses itself, it impales on the knife blades and is severed whereby full opening of the rupture disk without fragmentation is achieved.
A number of reverse buckling rupture disk assemblies having various parts and arrangements of such parts have been heretofore developed and used, but most of such assemblies utilize knife blades formed of at least three knife blade legs attached within the interior of the outlet rupture disk support member and positioned across the opening in said support member. For example, U.S. Pat. No. 3,294,277 issued to Wood on Dec. 27, 1966 and assigned to the assignee of the present invention discloses a reverse buckling rupture disk assembly including knife blade apparatus of the type described above. Another example of such an assembly is shown in U.S. Pat. No. 4,119,236 issued to Shaw et al. on Oct. 10, 1978.
In most of the heretofore developed rupture disk assemblies utilizing knife blades, the knife blade means are comprised of four sharpened blade legs of equal length having the interior ends thereof connected together at right angles and having the exterior ends welded to the interior of an annular rupture disk support member. In applications of rupture disk assemblies including such knife blade apparatus wherein the fluids relieved through the assemblies upon failure of the rupture disks thereof are extremely cold, cool upon expansion or are extremely hot, a problem has been encountered involving the breaking or cracking of the knife blade apparatus. That is, when the rupture disk in such an assembly ruptures and is severed by the knife blade means, cold fluid flowing through and being relieved by the rupture disk assembly quickly cools the knife blade means disposed in the outlet support member of the assembly causing the knife blade means to contract. Because, heretofore, the knife blade means have been rigidly attached to the outlet support member or to a secondary member which is rigidly held in the assembly, the knife blade means often crack, either in one or more of the blade legs or in one or more of the welds at the points of attachment of the blade legs to the support member. The rapid expansion of the knife blade means when contacted with hot fluid can also cause cracking or other damage to the knife blade means. Once cracked or otherwise damaged, the knife blade means and support member to which they are attached cannot be reused making the often frequent and expensive replacement of such apparatus necessary.
By the present invention an improved knife blade apparatus adapted to be installed in a rupture disk assembly is provided whereby failure of the knife blade apparatus due to the expansion or contraction thereof is obviated.